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bh=hiHo9DbDoCCDh4n5WrneTRby3gUfBpzNuKSPqTximSM=; b=HLXCp8dKfcXFlS+aG3GisBnY4m1UqmzHEy2ja6s7l72C1WWO3GwjEyvxubeR3OyIrgNDRD HD+C28F3WJqIFn4wHK4w9pVQbzVG7qF0uvAMV68CRGQmhXlekK/uMQT+ifc0BWwbsvgTj9 3yyzgMr+x6XhhWdrcqb1/XpEijuoObk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-459-CgSvLrj7O7-55ESvP_n3rw-1; Wed, 25 Nov 2020 08:08:40 -0500 X-MC-Unique: CgSvLrj7O7-55ESvP_n3rw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 75734100C66A; Wed, 25 Nov 2020 13:08:39 +0000 (UTC) Received: from work-vm (ovpn-115-12.ams2.redhat.com [10.36.115.12]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 715F85C1C5; Wed, 25 Nov 2020 13:08:28 +0000 (UTC) Date: Wed, 25 Nov 2020 13:08:25 +0000 From: "Dr. David Alan Gilbert" To: Andrey Gruzdev Subject: Re: [PATCH v3 3/7] support UFFD write fault processing in ram_save_iterate() Message-ID: <20201125130825.GE3222@work-vm> References: <20201119125940.20017-1-andrey.gruzdev@virtuozzo.com> <20201119125940.20017-4-andrey.gruzdev@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <20201119125940.20017-4-andrey.gruzdev@virtuozzo.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juan Quintela , qemu-devel@nongnu.org, Peter Xu , Markus Armbruster , Paolo Bonzini , Den Lunev Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Andrey Gruzdev (andrey.gruzdev@virtuozzo.com) wrote: > In this particular implementation the same single migration > thread is responsible for both normal linear dirty page > migration and procesing UFFD page fault events. > > Processing write faults includes reading UFFD file descriptor, > finding respective RAM block and saving faulting page to > the migration stream. After page has been saved, write protection > can be removed. Since asynchronous version of qemu_put_buffer() > is expected to be used to save pages, we also have to flush > migraion stream prior to un-protecting saved memory range. > > Write protection is being removed for any previously protected > memory chunk that has hit the migration stream. That's valid > for pages from linear page scan along with write fault pages. > > Signed-off-by: Andrey Gruzdev > --- > migration/ram.c | 124 ++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 115 insertions(+), 9 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index 7f273c9996..08a1d7a252 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -314,6 +314,8 @@ struct RAMState { > ram_addr_t last_page; > /* last ram version we have seen */ > uint32_t last_version; > + /* 'write-tracking' migration is enabled */ > + bool ram_wt_enabled; > /* We are in the first round */ > bool ram_bulk_stage; > /* The free page optimization is enabled */ > @@ -574,8 +576,6 @@ static int uffd_protect_memory(int uffd, hwaddr start, hwaddr length, bool wp) > return 0; > } > > -__attribute__ ((unused)) > -static int uffd_read_events(int uffd, struct uffd_msg *msgs, int count); > __attribute__ ((unused)) > static bool uffd_poll_events(int uffd, int tmo); > > @@ -1929,6 +1929,86 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss, > return pages; > } > > +/** > + * ram_find_block_by_host_address: find RAM block containing host page > + * > + * Returns true if RAM block is found and pss->block/page are > + * pointing to the given host page, false in case of an error > + * > + * @rs: current RAM state > + * @pss: page-search-status structure > + */ > +static bool ram_find_block_by_host_address(RAMState *rs, PageSearchStatus *pss, > + hwaddr page_address) > +{ > + bool found = false; > + > + pss->block = rs->last_seen_block; > + do { > + if (page_address >= (hwaddr) pss->block->host && > + (page_address + TARGET_PAGE_SIZE) <= > + ((hwaddr) pss->block->host + pss->block->used_length)) { > + pss->page = (unsigned long) > + ((page_address - (hwaddr) pss->block->host) >> TARGET_PAGE_BITS); > + found = true; > + break; > + } > + > + pss->block = QLIST_NEXT_RCU(pss->block, next); > + if (!pss->block) { > + /* Hit the end of the list */ > + pss->block = QLIST_FIRST_RCU(&ram_list.blocks); > + } > + } while (pss->block != rs->last_seen_block); > + > + rs->last_seen_block = pss->block; > + /* > + * Since we are in the same loop with ram_find_and_save_block(), > + * need to reset pss->complete_round after switching to > + * other block/page in pss. > + */ > + pss->complete_round = false; > + > + return found; > +} > + > +/** > + * get_fault_page: try to get next UFFD write fault page and, if pending fault > + * is found, put info about RAM block and block page into pss structure > + * > + * Returns true in case of UFFD write fault detected, false otherwise > + * > + * @rs: current RAM state > + * @pss: page-search-status structure > + * > + */ > +static bool get_fault_page(RAMState *rs, PageSearchStatus *pss) > +{ > + struct uffd_msg uffd_msg; > + hwaddr page_address; > + int res; > + > + if (!rs->ram_wt_enabled) { > + return false; > + } > + > + res = uffd_read_events(rs->uffdio_fd, &uffd_msg, 1); > + if (res <= 0) { > + return false; > + } > + > + page_address = uffd_msg.arg.pagefault.address; > + if (!ram_find_block_by_host_address(rs, pss, page_address)) { > + /* In case we couldn't find respective block, just unprotect faulting page */ > + uffd_protect_memory(rs->uffdio_fd, page_address, TARGET_PAGE_SIZE, false); > + error_report("ram_find_block_by_host_address() failed: address=0x%0lx", > + page_address); > + return false; > + } > + > + return true; > +} > + > /** > * ram_find_and_save_block: finds a dirty page and sends it to f > * > @@ -1955,25 +2035,50 @@ static int ram_find_and_save_block(RAMState *rs, bool last_stage) > return pages; > } > > + if (!rs->last_seen_block) { > + rs->last_seen_block = QLIST_FIRST_RCU(&ram_list.blocks); > + } > pss.block = rs->last_seen_block; > pss.page = rs->last_page; > pss.complete_round = false; > > - if (!pss.block) { > - pss.block = QLIST_FIRST_RCU(&ram_list.blocks); > - } > - > do { > + ram_addr_t page; > + ram_addr_t page_to; > + > again = true; > - found = get_queued_page(rs, &pss); > - > + /* In case of 'write-tracking' migration we first try > + * to poll UFFD and get write page fault event */ > + found = get_fault_page(rs, &pss); > + if (!found) { > + /* No trying to fetch something from the priority queue */ > + found = get_queued_page(rs, &pss); > + } > if (!found) { > /* priority queue empty, so just search for something dirty */ > found = find_dirty_block(rs, &pss, &again); > } > > if (found) { > + page = pss.page; > pages = ram_save_host_page(rs, &pss, last_stage); > + page_to = pss.page; > + > + /* Check if page is from UFFD-managed region */ > + if (pss.block->flags & RAM_UF_WRITEPROTECT) { > + hwaddr page_address = (hwaddr) pss.block->host + > + ((hwaddr) page << TARGET_PAGE_BITS); > + hwaddr run_length = (hwaddr) (page_to - page + 1) << TARGET_PAGE_BITS; > + int res; > + > + /* Flush async buffers before un-protect */ > + qemu_fflush(rs->f); > + /* Un-protect memory range */ > + res = uffd_protect_memory(rs->uffdio_fd, page_address, run_length, false); > + if (res < 0) { > + break; > + } > + } Please separate that out into a separate function. Dave > } > } while (!pages && again); > > @@ -2086,7 +2191,8 @@ static void ram_state_reset(RAMState *rs) > rs->last_sent_block = NULL; > rs->last_page = 0; > rs->last_version = ram_list.version; > - rs->ram_bulk_stage = true; > + rs->ram_wt_enabled = migrate_track_writes_ram(); > + rs->ram_bulk_stage = !rs->ram_wt_enabled; > rs->fpo_enabled = false; > } > > -- > 2.25.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK